Regulation of human cortical interneuron development by the chromatin remodeling protein CHD2

Mutations in the chromodomain helicase DNA binding protein 2 (CHD2) gene are associated with neurodevelopmental disorders. However, mechanisms by which CHD2 regulates human brain development remain largely uncharacterized. Here, we used a human embryonic stem cell model of cortical interneuron (hcIN) development to elucidate its roles in this process. We identified genome-wide CHD2 binding profiles during hcIN differentiation, defining direct CHD2 targets related to neurogenesis in hcIN progenitors and to neuronal function in hcINs. CHD2 bound sites were frequently coenriched with histone H3 lysine 27 acetylation (H3K27ac) and associated with high gene expression, indicating roles for CHD2 in promoting gene expression during hcIN development. Binding sites for different classes of transcription factors were enriched at CHD2 bound regions during differentiation, suggesting transcription factors that may cooperatively regulate stage-specific gene expression with CHD2. We also demonstrated that CHD2 haploinsufficiency altered CHD2 and H3K27ac coenrichment on chromatin and expression of associated genes, decreasing acetylation and expression of cell cycle genes while increasing acetylation and expression of neuronal genes, to cause precocious differentiation. Together, these data describe CHD2 direct targets and mechanisms by which CHD2 prevents precocious hcIN differentiation, which are likely to be disrupted by pathogenic CHD2 mutation to cause neurodevelopmental disorders.

Neuronal developmental gene and miRNA signatures induced by histone deacetylase inhibitors in human embryonic stem cells

Human embryonic stem cells (hESCs) may be applied to develop human-relevant sensitive in vitro test systems for monitoring developmental toxicants. The aim of this study was to identify potential developmental toxicity mechanisms of the histone deacetylase inhibitors (HDAC) valproic acid (VPA), suberoylanilide hydroxamic acid (SAHA) and trichostatin A (TSA) relevant to the in vivo condition using a hESC model in combination with specific differentiation protocols and genome-wide gene expression and microRNA profiling. Analysis of the gene expression data showed that VPA repressed neural tube and dorsal forebrain (OTX2, ISL1, EMX2 and SOX10)-related transcripts. In addition, VPA upregulates axonogenesis and ventral forebrain-associated genes, such as SLIT1, SEMA3A, DLX2/4 and GAD2. HDACi-induced expression of miR-378 and knockdown of miR-378 increases the expression of OTX2 and EMX2, which supports our hypothesis that HDACi targets forebrain markers through miR-378. In conclusion, multilineage differentiation in vitro test system is very sensitive for monitoring molecular activities relevant to in vivo neuronal developmental toxicity. Moreover, miR-378 seems to repress the expression of the OTX2 and EMX2 and therefore could be a regulator of the development of neural tube and dorsal forebrain neurons.

Characterisation of a neural teratogenicity assay based on human ESCs differentiation following exposure to valproic acid

The development of in vitro testing strategies for chemical and drug screening is a priority need in order to protect human health, to increase safety, to reduce the number of animals required for conventional testing methods and finally to meet the deadlines of current legislations. The aim of this work was to design an alternative testing method based on human embryonic stem cells for the detection of prenatal neural toxicity. For this purpose we have created a model based on the generation of neural rosettes, reproducing in vitro the gastrulation events recapitulating the formation of the neural tube in vivo. To validate the model we have exposed this complex cell system to increasing concentrations of valproic acid, a known teratogenic agent, to analyse the morphological and molecular changes induced by the toxicant. Specific assays were applied to discriminate between cytotoxicity and specific neural toxicity. Transcriptomic analysis was performed with a microarray Affimetrix platform and validated by quantitative real time RT-PCR for the expression of genes involved in early neural development, neural tube formation and neural cells migration, key biological processes in which the effect of valproic acid is most relevant. The results demonstrated that neural rosette cells respond to valproic acid exposure with molecular and morphological changes similar to those observed in vivo, indicating that this method represents a promising alternative test for the detection of human prenatal neural toxicity.

A tanscriptomics study to elucidate the toxicological mechanism of methylmercury chloride in a human stem cell based in vitro test

Traditional approaches in evaluating the hazard of drug candidates on the developing offspring are often time-consuming and cost-intensive. Moreover, variations in the toxicological response of different animal species to the tested substance cause severe problems when extrapolating safety dosages for humans. Therefore, more predictive and relevant toxicological systems based on human cell models are required. In the presented study the environmental toxicant methylmercury chloride (MeHgCl), known to cause structural developmental abnormalities in the brain, was used as reference compound to develop a concept contributing to a mechanistic understanding of the toxicity of an investigated substance. Despite the fact, that there are significant data available from animal studies and from poisonings in Japan and Iraq, uncertainties on the mechanism of MeHgCl during human development are still remaining and qualify the substance for further analysis. Transcriptomics analysis in combination with a human cell based in vitro model has been used in order to elucidate the toxicity of MeHgCl at molecular level. Differentiating neural precursor cells that have been exposed continuously to non- and low-cytotoxic concentrations of MeHgCl were investigated. Quantitative change in the mRNA expression profiles of selected genes demonstrated the sensitivity of the cell model and its qualification for a transcriptomics study screening changes in the expression profile of the complete human genome of MeHgCl-treated human neural cells. Potential biomarkers were identified and these candidate marker genes as well as their involvement in a possible toxic mechanism of MeHgCl during the human neurulation process are hereby introduced. The study confirmed the hypothesis that a cellular model based on a human stem cell line can be applied for elucidating unknown mode of actions of developmental toxicants.

Cytosine arabinoside induces ectoderm and inhibits mesoderm expression in human embryonic stem cells during multilineage differentiation

BACKGROUND AND PURPOSE

Teratogenic substances induce adverse effects during the development of the embryo. Multilineage differentiation of human embryonic stem cells (hESCs) mimics the development of the embryo in vitro. Here, we propose a transcriptomic approach in hESCs for monitoring specific toxic effects of compounds as an alternative to traditional time-consuming and cost-intensive in vivo tests requiring large numbers of animals. This study was undertaken to explore the adverse effects of cytosine arabinoside (Ara-C) on randomly differentiated hESCs.

EXPERIMENTAL APPROACH

Human embryonic stem cells were used to investigate the effects of a developmental toxicant Ara-C. Sublethal concentrations of Ara-C were given for two time points, day 7 and day 14 during the differentiation. Gene expression was assessed with microarrays to determine the dysregulated transcripts in presence of Ara-C.

KEY RESULTS

Randomly differentiated hESCs were able to generate the multilineage markers. The low concentration of Ara-C (1 nM) induced the ectoderm and inhibited the mesoderm at day 14. The induction of ectodermal markers such as MAP2, TUBB III, PAX6, TH and NESTIN was observed with an inhibition of mesodermal markers such as HAND2, PITX2, GATA5, MYL4, TNNT2, COL1A1 and COL1A2. In addition, no induction of apoptosis was observed. Gene ontology revealed unique dysregulated biological process related to neuronal differentiation and mesoderm development. Pathway analysis showed the axon guidance pathway to be dysregulated.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that hESCs in combination with toxicogenomics offer a sensitive in vitro developmental toxicity model as an alternative to traditional animal experiments.